A novel evolution scheme from legacy TDM-PON to the next generation WDM-PON with DPSK/ASK orthogonal modulation is proposed. The new WDM-PON is added into the existing PON infrastructure and coexisting with the current TDM-PON. To eliminate any change requirement for the existing TDM-PON, DPSK is applied for WDM-PON downstream. Meanwhile, upstream remodualtion is applied to achieve colorless ONU in WDM-PON. The application of DPSK/ASK reduces both crosstalk from coexisting and remodulation. The experiment results show the crosstalk is very little. Good performance is achieved for both unchanged coexisting TDM-PON and WDM-PON upstream signals in our proposed scheme.